Efflorescence is known in particular in the case of cement-based building materials such as concrete, plasters, and mortars. The skilled person means by efflorescence whitish deposits on the surface, which are formed above all as a result of liberated calcium hydroxide, which continues to react by means of carbon dioxide from the air to calcium carbonate. Further salt deposites may also be included in this process. Although such efflorescence as a rule does not have any noteworthy effect on the physical properties of the substrate, it is still considered to be very annoying especially in the case of colored or grey surfaces.
To solve this problem several suggestions are made in WO 2001/72658 A1, WO 2005/097699 A1, and also in WO 2006/094528 A1 and WO 2006/094809 A1 to formulate the mortar composition accordingly by means of specific selection of the mineral binder components. It is true that as a result of this the efflorescence could be reduced, but for the formulator the possibility of setting the property profile as desired precisely by changing these components, such as for instance setting behavior, pot life, open time and/or shrinkage behavior, of the mortar to be formulated, is greatly reduced.
In another approach additives are mentioned the addition of which to hydraulically setting building materials should prevent or reduce efflorescence. Thus for instance GB 1,088,485 A mentions that an aqueous dispersion of a mixture of tall oil resin and high-boiling fractions of tall oil, in part also mixed with asphalt, can either be mixed into the concrete or be applied on the surface subsequently. The process for the preparation of such dispersions is very complicated and hence expensive, with the dark to black color of the mixture substantially restricting its range of application. In DE 33 21 027 A1 a process is described in which inter alia also a reduction of efflorescence and a decrease of the water absorption should occur. In this process use is made of terpene polymers, in particular of liquid low-molecular terpenes, alone or mixed with other terpene hydrocarbons, which are added to the cement-containing building materials in an amount of 0.1-10 wt. %. The addition of the terpene-based compounds takes place in emulsified form or by spraying of liquid or dissolved terpenes, which renders its use in inter alia dry mortars impossible. Furthermore, EP 1 767 506 A1 describes a water-redispersible powder for the reduction of efflorescence in hydraulically set building materials, consisting of at least one organic component and at least one water-soluble organic polymeric protective colloid, where the organic component contains at least one compound with a cyclic group which is fully or partially saturated, has a melting point of about −20 to 250° C. and a molecular weight of about 100 to 10,000, and forms a stable dispersion with the water-soluble organic polymeric protective colloid in water.
GB 2,343,448 A describes concrete for walls with improved resistance to freeze-thaw, where also additives to control efflorescence can be added thereto. As such additives are mentioned calcium stearate, fatty acids and the salts thereof, polyvinyl alcohol, water-based latices, silanes, siloxanes and mixtures thereof. In order to give the concrete for walls sufficient strength, small amounts of a betaine are added.
US 2005/0106336 A1 and WO 2005/014256 A1 describe composite materials which are suitable for the production of cement-based slabs, where a material with antimicrobial properties is added. As antimicrobial compounds organic and inorganic agents may be used. Quaternary ammonium compounds are a preferred class. Efflorescence is not mentioned.
In published application DE 26 36 271 a process for the preparation of a light mortar with a predominant volume share of expanded perlite is described. To this are besides perlite also added cement and in about the same amount calcium hydroxide or calcium oxide and a tenside. The tenside to be used preferably is of an anionic nature, but can also be of a cationic or non-ionic nature. There is no mention of efflorescence.
Because of the substantially different fields of application of mortars and concretes, these also have a very different composition. It should be added that for instance another cement, be it of a different production type or a different quality, can show quite different efflorescence behavior. The climatic conditions also play an important part in whether an applied building material has a tendency to efflorescence or not. In accordance with the plurality of different compositions of concrete and mortar it has become apparent that it is of great advantage when the formulator can choose from different materials for the reduction of efflorescence, in order to select the most suitable product for the specific recipe in each case.
Thus the problem presented itself of providing an additive which eliminates or at least very strongly reduces the efflorescence of building materials, in particular in hydraulically setting building materials, such as for instance cement-based mortars and concretes. Moreover, it should be possible for the additive to be present in powder form, in particular for the formulation of dry mortars, in order to avoid the well-known disadvantages of liquid raw materials such as for instance lack of resistance to freeze-thaw or limited storage stability without the addition of toxic biocides, and to make possible simple dosing in the case of dry mortar formulations. Moreover, it is essential that this additive can be easily introduced into the mortar matrix which is mixed or to be mixed with water, without special mixing processes having to be taken into account. The additive should be very readily wettable, redispersible or soluble in the mortar mixture and should have easy and homogeneous distribution in the matrix. It is also important that no disadvantageous or quite different mortar properties are obtained with the additive, i.e. it should be possible to introduce the additive into existing mortar formulations without the properties thereof being altered, except for the desired substantial reduction of the efflorescence effect. Moreover, it to should be possible to dose the additive independent of other mortar raw materials, which allows the formulator a very high flexibility. Further it is important that the raw material and preparation costs of the dry mortar do not change or change only to a slight extent because of the additive.